Researchers at security specialist ESET claim to have found a shiny new advanced persistent threat (APT) group dubbed FamousSparrow – after discovering its custom backdoor, SparrowDoor, on hotels and government systems around the world.
“FamousSparrow is currently the only user of a custom backdoor that we discovered in the investigation and called SparrowDoor,” ESET researcher and co-author of the report Tahseen Bin Taj explained in a prepared statement. “The group also uses two custom versions of Mimikatz. The presence of any of these custom malicious tools could be used to connect incidents to FamousSparrow.”
The group can be traced back to 2019, the researchers claimed, though the attacks tracked in the report made use of the ProxyLogon vulnerability in Microsoft Exchange starting in March this year. Victims were spread around Europe, the Middle East, the Americas, Asia, and Africa – without a single one being discovered in the US, oddly.
Another interesting wrinkle comes from its focus. With ESET’s researchers suggesting the group’s attacks are for the purpose of espionage, it’s no surprise to see government organisations, engineering firms, and law offices among those targeted – but the majority of its victims were hotels, the report found.
It’s not entirely certain that FamousSparrow represents a wholly new APT group. While the SparrowDoor tool appears to be exclusive and suggests a new player, the researchers found potential links between FamousSparrow and existing APT groups – including the use of the Motnug loader known to have been used by a group dubbed SparklingGoblin and a SparrowDoor-compromised machine seen to be connecting to a command and control server connected to the DRDControl group.
FamousSparrow is also far from the only group taking advantage of the ProxyLogon vulnerability, with researchers having linked its use to more than ten APT groups – most of which, like FamousSparrow, began their attacks the day after Microsoft had released patches, taking advantage of the window between the release of a patch and its widespread installation.
The group revealed that it had detected around 20 infections worldwide.
“This is another reminder that it is critical to patch internet-facing applications quickly,” report co-author Matthieu Faou, who discovered the backdoor with fellow ESET researcher Bin Taj, advised for those looking to protect themselves from the group and others, “or, if quick patching is not possible, to not expose them to the internet at all.”
We asked how likely it was that FamousSparrow was a wholly new group, rather than an existing group using a new tool. ESET researcher Matthieu Faou responded: “We did not find enough evidence to link FamousSparrow to another threat group. This doesn’t necessarily mean FamousSparrow was created recently. They could have stayed undetected for years or they could be a known group that evolved and retooled so much that we could not find a link to their previous activities.”
As to why the group is primarily targeting hotels, Faou told us: “Hotels are interesting for cyber-espionage groups because it allows them to track the travel of their targets and, by infiltrating the network of the hotels, they could potentially spy on the network traffic of people staying at these hotels.” He added: “Even though FamousSparrow compromised a lot of hotels, they’ve also breached several governments.”
Would it be possible to exploit the kill-switch in the backdoor to remove it? Faou said: “The kill-switch is intended to be used by the operators only. The command 0x12635692 should be sent by the C&C server to terminate SparrowDoor. Unless someone takes control of the C&C server and sends the kill command, there is no way of exploiting it to clean the compromised machines.” How can businesses protect themselves from FamousSparrow attack? The ESET researcher told us: “For most of the victims, the initial intrusion vector was a web server unpatched and exposed to the internet. This is another reminder that complex web applications such Microsoft Exchange should be patched quickly and if possible, not exposed to the internet.”
The full report, which goes into detail on the loader’s operation and the backdoor’s capabilities and offers multiple indicators of a compromised system, is available on the ESET research blog. The company has also published samples and additional indicators to GitHub. ®